1. Field of the Invention
The present invention relates generally to electrical switching apparatus and, more particularly, to a locking assembly for the operating handle of a circuit breaker.
2. Background Information
Electrical switching apparatus include, for example, circuit switching devices and circuit interrupters such as circuit breakers, contactors, motor starters, motor controllers and other load controllers.
Circuit breakers are generally old and well known in the art. An example of a circuit breaker is disclosed in U.S. Pat. No. 5,341,191. Circuit breakers are used to protect electrical circuitry and equipment from damage due to an over current condition, such as an overload condition or a relatively high level short circuit or fault condition. Molded case circuit breakers, for example, include at least one pair of separable contacts which are operated either manually by way of a handle disposed on the outside of the case or automatically by way of an internal trip unit in response to an over current condition.
Circuit breakers typically have two or three possible operating handle positions, corresponding to the status of the separable contacts. For example, these positions may include an ON position, in which the separable contacts are closed, an OFF position in which the contacts are open, and a tripped position in which the contacts are tripped open. Typically, the handle position corresponding to the tripped position of the contacts is in between the ON and OFF positions.
In circuit breaker installations, for example in a panel board or load center, it is often desirable or essential that the settings of a single circuit breaker, or a group of circuit breakers, remain undisturbed. Unauthorized or inadvertent changing of the position of these breakers could result in annoying interruptions to service or operations, serious damage to an electrical apparatus, or even serious harm to a person. For example, accidental actuation of a circuit breaker might result in electrocution or shock to a workman performing electrical work or repair on equipment downstream from the circuit breaker. Therefore, to prevent, for example, another person from inadvertently returning the circuit breaker handle to the ON position when a worker is doing electrical work in an area other than the immediate vicinity of the circuit breaker box or electrical panel, safety measures must be taken. One such safety measure is the addition of a locking assembly to prevent displacement of the circuit breaker operating handle.
U.S. Pat. Nos. 2,849,552; 3,214,530; 3,408,466; 4,347,412; 5,147,991; 5,219,070; 5,310,969; 5,412,167; 5,500,495; 5,577,599; 5,732,815; 5,817,998; and 5,817,999 disclose handle locking mechanisms consisting of an assembly of at least two parts and each employs a padlock to lock the handle of the circuit breaker in a fixed position. There are several disadvantages associated with known handle locking mechanisms of this type.
One problematic attribute of such locking provisions is the possibility of creating an unintentional lock-ON condition. For example, many known locking assemblies of this type permit the padlock to engage the assembly (i.e., inserting the hasp of the padlock through a receiving opening in one or more locking assembly components) when the circuit breaker handle is in the ON position. The engaged lock can prevent the circuit breaker handle or other operating mechanism from achieving sufficient rotation or movement to open the circuit. Moreover, although known locking assemblies of this type are generally only intended to lock the handle in the OFF position, most can just as easily lock the handle in the ON position by inadvertently reversing the direction in which the assembly is attached to the handle. Accidentally locking the handle in the ON position creates an unsafe condition by hampering emergency shut-off of the equipment.
There are a number of known variations of these types of locking mechanisms. For example, many such locking mechanisms employ a set or Allen screw to engage the circuit breaker handle, in order to prohibit its movement. See, e.g., U.S. Pat. Nos. 2,849,552; 5,147,991; 5,500,495; and 5,732,815. Construction of the locking mechanisms is typically complex and often comprises numerous, separate parts. Generally, the locking mechanisms are not integrated with the circuit breaker, thereby being susceptible to loss of one or more pieces when not in use. Applicability is often limited to a certain type of circuit breaker or a select type or shape of circuit breaker handle. See, e.g., U.S. Pat. Nos. 3,408,466; 4,347,412; 5,219,070; 5,412,167; and 5,817,999. Many known locking mechanisms of this type also employ at least one nose, wedge, end part, leg or similar structure adapted for insertion within the handle opening of the circuit breaker housing, for example, between the circuit breaker handle and the end wall of the handle opening, to abut, underlie or otherwise engage the end wall, in order to resist movement of the circuit breaker handle. See, e.g., U.S. Pat. Nos. 2,849,552; 3,408,466; 4,347,412; 5,412,167; 5,500,495; 5,732,815; and 5,817,998.
As shown in FIG. 1, another known locking assembly 2 attempts to overcome the aforementioned disadvantage by employing a slider plate assembly 4 attached to the circuit breaker operating handle 6 and a separate fixed shroud 8 overlying the operating handle 6 and slider plate assembly 4. The slider plate assembly 4 includes an elongated laterally extending portion 10 and a tab projection 12, which projects perpendicularly from the operating handle 6. The fixed shroud 8 includes an elongated lock-OFF opening 14 for receiving the hasp 16 of the padlock 18 and a slot 20 for receiving the tab projection 12 of the slider plate assembly 4 when the circuit breaker operating handle 6 is in the OFF position, as shown. The circuit breaker operating handle 6 includes an elongated, laterally extending portion 22 with a lock-OFF opening 24. This elongated laterally extending portion 22 corresponds to the laterally extending portion 10 of the slider plate assembly 4. Unless the operating handle 6 is in the OFF position (as shown) and the slider plate 4 is pushed upward (as shown in phantom line drawing in FIG. 1), against the force of gravity until the tab projection 12 is received in the slot 20 on the fixed shroud 8 (see, e.g., tab projection 12 of slider plate assembly 4 shown in phantom line drawing in FIG. 1), the elongated laterally extending portion 10 of the slider plate assembly 4 blocks the lock-OFF openings 14, 24 of both the fixed shroud 8 and the operating handle 6. Then, in order to lock the handle 6 in the OFF position, as shown, the slider plate 4 must be held in the upward position (see, e.g., tab projection 12 shown in phantom line drawing disposed in the upward position within slot 20 in FIG. 1) while the hasp 16 of the padlock 18 is inserted through the corresponding lock-OFF openings 14, 24. This locking assembly 2 continues to require numerous complex moving parts and the manual manipulation of at least the slider plate assembly 4, in order to permit the operating handle 6 to be locked in the OFF position.
Accordingly, there is room for improvement in electrical switching apparatus and operating handle locking assemblies for electrical switching apparatus.